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This invention relates in general to a method and apparatus for tracking items using radio frequency identification tags and, more particularly, to such a method and apparatus which facilitates accuracy in the determination of the location of the items.
According to an existing technique for tracking items, a device known as a radio frequency identification tag is mounted on each item, and radio frequency signals are used to communicate information from the tag to a receiver, which is referred to as a reader. The tag may be active or passive. Although existing tags and the systems that use them have been generally adequate for their intended purposes, they have not been satisfactory in all respects.
In this regard, there are situations in which, as to determination of the specific location of the item which bears the tag, it is desirable to have a higher degree of accuracy than can be achieved with existing tags. For example, existing tags may determine the distance to the device based on the magnitude of the signal emitted by the tag, as received at the reader. However, similar existing tags may transmit signals with slightly different magnitudes, and environmental factors may affect the magnitude of the signals transmitted by these tags. As a result, there is a fair margin of error in the ability of the reader to accurately determine the distance to a tag based on the magnitude of the received signal.
Further, it may be even more difficult for the reader to determine the direction to the tag. In fact, it is typically necessary to provide multiple readers at spaced locations, and to use a form of triangulation based on the magnitudes of the signals received at two or three of the readers, in order to attempt to determine the direction to the tag from each of the readers.
From the foregoing, it may be appreciated that a need has arisen for a method and apparatus for using a tag to track an item, in which the location of the item can be determined with a relatively high degree of accuracy. According to the present invention, a method and apparatus are provided to address this need and involve: receiving in a receiver section of a tag wireless signpost signals that each include a signpost code, the wireless signpost signals being near field signals of primarily magnetic character; and transmitting from a transmitter section of the tag wireless beacon signals which each include a beacon code associated with the tag, the transmitting step including the step of causing the transmitter section to be responsive to receipt by the receiver section of a respective signpost signal for including in at least one beacon signal the signpost code from the received signpost signal.